Vibration sensor

ABSTRACT

A vibration sensor capable of preventing a diaphragm electrode from being damaged without lowering sensitivity as well as realizing a satisfactory assembling process. The vibration sensor includes a fixed electrode  1 , and a diaphragm electrode  3  having a weight member  2  attached to a membrane surface facing away from the fixed electrode  1  and fixedly supported at peripheries thereof, the vibration sensor being capable of outputting variation of capacitance between the fixed electrode and the diaphragm electrode as vibration signals. The vibration sensor further includes projecting portions  2   a  formed on parts of an end portion of the weight member  2  to project along the direction of the membrane surface and spaced from the membrane surface of the diaphragm electrode  3 , and a restricting member  4  for contacting the projecting portions  2   a  of the weight member  2  displaced along the direction of the membrane surface of the diaphragm electrode  3 , thereby to restrict displacement of the weight member  2.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vibration sensor comprising a fixedelectrode, and a diaphragm electrode having a weight member attached toa membrane surface facing away from the fixed electrode and fixedlysupported at peripheries thereof, the vibration sensor being capable ofoutputting variations of capacitance between the fixed electrode and thediaphragm electrode as vibration signals.

2. Description of Related Art

The above-noted vibration sensor is a vibration sensor of the electretcondenser microphone type (ECM type) usable for a pedometer, forexample. Conventionally, a weight member in the form of a thincylindrical member or the like is attached to the diaphragm electrode inorder to detect low frequency vibrations generated in time of walkingand the like. Also, a relatively large gap is defined between an endportion of the plate-shaped weight member and a diaphragm ring fixedlysupporting the diaphragm electrode at peripheries thereof, or betweenthe weight member and a circuit board arranged on a back side of theweight member (see Patent Document 1 and Patent Document 2, forexample).

Patent Document 1: Patent Application “Kokai” No. 59-70700

Patent Document 2: Patent Application “Kokai” No. 10-9944

SUMMARY OF THE INVENTION

However, as noted above, a relatively large gap is defined between theend portion of the weight member and the diaphragm ring, or between theweight member and the circuit board, which incurs a risk of damaging thesensor by a great force applied to the diaphragm electrode when thesensor is dropped to receive an excessive shock to the point of movingthe weight member by a large amount. Specifically, when the weightmember has a sharp corner portion at the end portion thereof, such anend corner portion contacts and easily damages the diaphragm electrodewhen the weight member is attached to the diaphragm electrode. Also, thediaphragm electrode is easily damaged by stress concentration when ashock is applied.

On the other hand, it is possible to increase an inertial force byincreasing the weight of the weight member thereby to enhance thesensitivity of the sensor. However, it is not advantageous to merelyincrease the diameter of the cylindrical weight member because the widthof a movable portion formed outwardly of the diaphragm electrode isreduced even though the weight is increased. When the height of thecylindrical weight member is increased, the moment caused by a shockoccurring when the sensor is dropped or the like is also increased, as aresult of which the diaphragm electrode is easily damaged.

The present invention has been made having regard to the above-notedproblems, and its object is to provide a vibration sensor capable ofpreventing a diaphragm electrode from being damaged without loweringsensitivity, as well as realizing a satisfactory assembling process.

In order to achieve the above object, a first characteristic feature ofa vibration sensor according to the present invention lies in comprisinga fixed electrode, and a diaphragm electrode having a weight memberattached to a membrane surface facing away from the fixed electrode andfixedly supported at peripheries thereof, the vibration sensor beingcapable of outputting variations of capacitance between the fixedelectrode and the diaphragm electrode as vibration signals, wherein thevibration sensor further comprises projecting portions formed on partsof an end portion of the weight member to project along a direction ofthe membrane surface and spaced from the membrane surface of thediaphragm electrode, and a restricting member for contacting theprojecting portions of the weight member displaced along the directionof the membrane surface of the diaphragm electrode thereby to restrictdisplacement of the weight member.

When the weight member receives a shock, as the sensor is dropped, to bedisplaced along a direction of the membrane surface of the diaphragmelectrode, the projecting portions formed on the end portion of theweight member contact the restricting member thereby to restrict a largedisplacement of the weight member. Thus, the diaphragm electrode isprevented from being damaged by displacement of the weight member alongthe direction of the membrane surface.

On the other hand, the projecting portions project along the directionof the membrane surface and are spaced from the membrane surface of thediaphragm electrode to secure a movable portion in the diaphragmelectrode between the portion where the end portion of the weight memberis attached and the fixed peripheral portion. Thus, the weight member isnot prevented from moving along directions perpendicular to thedirection of the membrane surface of the diaphragm electrode byvibrations to be detected, thereby avoiding a lowering of sensitivity.The sensitivity is improved by the increase in the weight of the weightmember due to formation of the projecting portions.

Further, the projecting portions are formed on parts of the end portionof the weight member and not formed on the entire end portion to producea gap between the end portion having no projecting portion and therestricting member. Air enters and exits through the gap when the weightmember is moved, thereby to allow a smooth movement of the weightmember. Thus, a lowering of sensitivity can be avoided.

At the same time, since the projecting portions are formed on parts ofthe end portion of the weight member, it is possible to position theweight member relative to the diaphragm electrode while the weightmember is held by a jig or the like inserted into the gap between theend portion of the weight member having no projecting portion and therestricting member in time of attaching the weight member to thediaphragm electrode. By contrast, it would be difficult to position theweight member while being held, where the projecting portions are formedon the entire end portion of the weight member.

Hence, it is possible to provide the vibration sensor capable ofpreventing damage to the diaphragm electrode while avoiding a loweringof sensitivity, and also allowing a satisfactory assembling process.

A second characteristic feature of the vibration sensor according to thepresent invention lies in comprising a fixed electrode, and a diaphragmelectrode having a weight member attached to a membrane surface facingaway from the fixed electrode and fixedly supported at peripheriesthereof, the vibration sensor being capable of outputting variations ofcapacitance between the fixed electrode and the diaphragm electrode asvibration signals, wherein the vibration sensor further comprisesrestricting members for contacting end portion of the weight memberdisplaced along the direction of the membrane surface of the diaphragmelectrode, thereby to restrict displacement of the weight member, therestricting members being formed on parts opposed to the end portion ofthe weight member and spaced from the membrane surface of the diaphragmelectrode.

When the weight member receives a shock, as the sensor is dropped, to bedisplaced along a direction of the membrane surface of the diaphragmelectrode, the end portion of the weight member contacts the restrictingmembers, thereby to restrict a large displacement of the weight member.Thus, the diaphragm electrode is prevented from being damaged bydisplacement of the weight member along the direction of the membranesurface.

On the other hand, the restricting members are arranged to be spacedfrom the membrane surface of the diaphragm electrode to secure a movableportion in the diaphragm electrode between the portion where the endportion of the weight member is attached and the fixed peripheralportion. Thus, the weight member is not prevented from moving along thedirections perpendicular to the direction of the membrane surface of thediaphragm electrode by vibrations to be detected, thereby avoiding alowering of sensitivity.

Further, the restricting members are formed on parts opposed to the endportion of the weight member and not opposed to the entire end portionto produce gaps between the end portion having no restricting member andthe restricting members. Air enters and exits through the gaps when theweight member is moved to allow a smooth movement of the weight member,thereby avoiding a lowering of sensitivity.

At the same time, since the restricting members are formed on partsopposed to the end portion of the weight member, it is possible toposition the weight member relative to the diaphragm electrode while theweight member is held by a jig or the like inserted into a gap betweenthe end portion of the weight member and the restricting members in timeof attaching the weight member to the diaphragm electrode. By contrast,it would be difficult to position the weight member while being held,where the restricting members are opposed to the entire end portion ofthe weight member.

Hence, it is possible to provide the vibration sensor capable ofpreventing damage to the diaphragm electrode while avoiding a loweringof sensitivity, and also allowing a satisfactory assembling process.

A third characteristic feature of the vibration sensor according to thepresent invention lies in that, in addition to the above first or secondfeature, the sensor further comprises a second restricting member forcontacting a surface of the weight member displaced along a directionperpendicular to the membrane surface of the diaphragm electrode,thereby to restrict displacement of the weight member.

When the weight member receives a shock, as the sensor is dropped, to bedisplaced excessively in a direction perpendicular to the membranesurface of the diaphragm electrode, the surface of the weight membercontacts the second restricting member to restrict displacement of theweight member. Thus, the diaphragm electrode is prevented from beingdamaged by excessive displacement of the weight member in the directionperpendicular to the membrane surface.

Hence, a further preferred embodiment of the vibration sensor isprovided which is capable of preventing the diaphragm electrode frombeing damaged by displacement of the weight member along the directionperpendicular to the membrane surface as well as displacement of theweight member along the direction of the membrane surface.

A fourth characteristic feature of the vibration sensor according to thepresent invention lies in that, in addition to the above third feature,the sensor further comprises a circuit board having an output circuitmounted thereon for vibration signals, wherein the circuit board or anelectronic part mounted on the circuit board acts also as the secondrestricting member.

When the circuit board having the output circuit for outputtingvariations of capacitance between the fixed electrode and the diaphragmelectrode as vibration signals is provided within the sensor, thecircuit board per se or the electronic parts mounted on the circuitboard acts as the second restricting member as well. Thus, any secondrestricting member for exclusive use is dispensable thereby to simplifythe construction.

Hence, a further preferred embodiment is provided which is capable ofpreventing the diaphragm electrode from being damaged by displacement ofthe weight member along the direction perpendicular to the membranesurface through the simplified construction.

A fifth characteristic feature of the vibration sensor according to thepresent invention lies in comprising a fixed electrode, and a diaphragmelectrode having a weight member attached to a membrane surface facingaway from the fixed electrode and fixedly supported at peripheriesthereof, the vibration sensor being capable of outputting variations ofcapacitance between the fixed electrode and the diaphragm electrode asvibration signals, wherein the weight member includes a corner portioncontacting the diaphragm electrode and having a sectional shape formingan obtuse angle with the membrane surface of the diaphragm electrode.

When the sensor is dropped and the weight member receives a shock to bedisplaced, the corner portion of the end portion of the weight membercontacting the diaphragm electrode is pressed against the diaphragmelectrode. Since the corner portion has a sectional shape forming anobtuse angle with the membrane surface of the diaphragm electrode, thecorner portion formed on the end portion of the weight member contactsthe membrane surface of the diaphragm electrode softly, which can avoida stress concentration on a part of the diaphragm electrode, thereby toavoid damage to the diaphragm electrode. At this time, a movable portionis secured in the diaphragm electrode between the portion where the endportion of the weight member is attached and the fixed peripheralportion, which does not hinder movement of the weight member operated byvibrations to be detected. Thus, sensitivity is not lowered.

Hence, it is possible to provide the vibration sensor capable ofpreventing the diaphragm electrode from being damaged while avoiding alowering of sensitivity.

A sixth characteristic feature of the vibration sensor according to thepresent invention lies in comprising a fixed electrode, and a diaphragmelectrode having a weight member attached to a membrane surface facingaway from the fixed electrode and fixedly supported at peripheriesthereof, the vibration sensor being capable of outputting variations ofcapacitance between the fixed electrode and the diaphragm electrode asvibration signals, wherein the diaphragm electrode includes a corrugatedportion between an inner portion where the weight member is attached andan outer portion fixedly supported.

When the sensor is dropped and the weight member receives a shock to bedisplaced, the corrugated portion formed on the diaphragm electrodebetween the inner portion where the weight member is attached and theouter portion fixedly supported extends and contracts in the directionsof the membrane surface of the diaphragm electrode, or oscillates indirections perpendicular to the membrane surface of the diaphragmelectrode, thereby to absorb excessive displacements of the weightmember caused by the shock. Thus, it can avoid am stress concentrationon the diaphragm electrode and prevent the diaphragm electrode frombeing damaged. At the same time, the corrugated portion can secure amovable portion for the diaphragm electrode, which allows a smoothmovement of the weight member operated by vibrations to be detected andperforms an effect of increasing sensitivity.

Hence, it is possible to provide the vibration sensor capable ofpreventing the diaphragm electrode from being damaged, while avoiding alowering of sensitivity.

BRIEF DESCRIPTION Of The DRAWINGS

FIG. 1 A sectional view showing a construction of a vibration sensoraccording to a first embodiment.

FIG. 2 Plan views and sectional views showing the construction of thevibration sensor according to the first embodiment.

FIG. 3 A sectional view showing a construction of a vibration sensoraccording to a second embodiment.

FIG. 4 A sectional view showing a modified construction of the vibrationsensor according to the second embodiment.

FIG. 5 A schematic diagram showing an output circuit for vibrationsignals of the vibration sensor according to the second embodiment.

FIG. 6 A sectional view showing a modified construction of the vibrationsensor according to the second embodiment.

FIG. 7 A sectional view showing a construction of a vibration sensoraccording to the third embodiment.

FIG. 8 A sectional view showing a construction of a vibration sensoraccording to a fourth embodiment.

FIG. 9 Plan views and sectional views showing the construction of thevibration sensor according to the fourth embodiment.

FIG. 10 Sectional views showing constructions of vibration sensorsaccording to further embodiments.

DESCRIPTION Of PREFERRED EMBODIMENTS

Vibration sensors embodying the present invention will be described withreference to the drawings.

First Embodiment

As shown in FIG. 1, a vibration sensor according to a first embodimentcomprises a fixed electrode 1, and a diaphragm electrode 3 having aweight member 2 in the form of a thin cylindrical member attached to amembrane surface facing away from the fixed electrode 1 and fixedlysupported at peripheries thereof. The vibration sensor is capable ofoutputting variations of capacitance between the fixed electrode 1 andthe diaphragm electrode 3 as vibration signals. Projecting portions 2 aare formed on parts of an end portion of the weight member 2 to projectalong the direction of the membrane surface and spaced from the membranesurface of the diaphragm electrode 3. A diaphragm ring 4 is mountedadjacent the end portion of the weight member 2 for contacting theprojecting portions 2 a of the weight member 2 displaced along thedirection of the membrane surface of the diaphragm electrode 3 to act asa restricting member for restricting displacement of the weight member2.

The above-noted fixed electrode 1 is provided by a bottom portion of ahousing 10 having a U-shaped section with an electret layer 5 formed onan inner surface thereof. Successively stacked on the bottom portion ofthe housing 10 are a ring-shaped plastic spacer 6, the above diaphragmelectrode 3, the diaphragm ring 4 and an electrode ring 7. Then, theweight member 2 is inserted into an inner space of the diaphragm ring 4and applied to the diaphragm electrode 3. Lastly, the housing 10 iscovered with and secured to a circuit board 8 having an output circuitmounted thereon for vibration signals, thereby to assemble the vibrationsensor. In this arrangement, the diaphragm electrode 3 is fixedlysupported and held between the spacer 6 and the diaphragm ring 4 at theperipheries thereof. The housing 10, the diaphragm ring 4 and theelectrode ring 7 are made of metal.

The diaphragm electrode 3 comprises an electrode layer formed of a highpolymer resin film material of approximately 2 micrometers in thickness,for example, and having one surface (the lower surface in FIG. 1) coatedwith a metal such as Ni, Al, Ti or the like by vapor evaporation. Theelectrode layer allows the diaphragm electrode 3 to be conductive withthe diaphragm ring 4.

The projecting portions 2 a formed on parts of the end portion of theweight member 2, specifically, are formed as three claw-shaped portionsarranged in positions of rotational symmetry of 120 degrees around theend portion of the weight member 2 having a cylindrical shape in planview as shown in FIG. 2( a), or as a flange-shaped portion having twocutout portions p opposed to each other in a plate-surface directionover the entire circumference of the end portion of the weight member 2having a cylindrical shape in plan view as shown in FIG. 2( b).Therefore, it is possible to place a jig such as tweezers to contact theend portion of the weight member 2 in positions other than theclaw-shaped portions or the flange-shaped portions thereby to hold theweight member 2. In this condition, the weight member 2 is inserted intothe inner space of the diaphragm ring 4 and positioned in place to beapplied to the diaphragm electrode 3.

Further, as illustrated in FIG. 1, the weight member 2 has a cornerportion 2 b contacting the diaphragm electrode 3 and having a sectionalshape forming an obtuse angle with the membrane surface of the diaphragmelectrode 3. In the drawing, one example of the corner portion 2 b isshown as a curved portion where the angle is gradually varied (sagged).Instead, the corner portion 2 b may be chamfered.

Second Embodiment

A vibration sensor according to a second embodiment of the presentinvention is different from that of the first embodiment in that theformer provides a construction for restricting displacement of theweight member 2 in directions perpendicular to the membrane surface ofthe diaphragm electrode 3 in addition to displacement of the weightmember 2 in the directions along the membrane surface of the diaphragmelectrode 3.

More particularly, as illustrated in FIG. 3, a limit ring 9 is providedacting as a second restricting member KB for contacting a surface 2 c ofthe weight member 2 displaced along directions perpendicular to themembrane surface of the diaphragm electrode 3, thereby to restrictdisplacement of the weight member 2. The limit ring 9 is arranged to besandwiched between the diaphragm ring 4 and the electrode ring 7 and hasan opening formed in the center thereof. Thus, air enters and exitsthrough the opening of the limit ring 9 smoothly, which diminishesviscosity resistance (stiffness) of the diaphragm electrode 3 in time ofdisplacement thereof thereby to increase amplitude.

FIG. 4 and FIG. 6 show modified constructions of the vibration sensoraccording to the second embodiment.

With reference to FIG. 4, the circuit board 8 having the output circuitfor vibration signals includes electronic parts 8 a mounted thereonwhich act also as the second restricting member KB. The electronic partsinclude passive components such as a chip resistor and a chip condenser,active components such as a transistor and an FET (field effecttransistor), an IC (integrated circuit) and the like. FIG. 5 shows aschematic diagram of the output circuit for vibration signals. Thecircuit board 8 has only a chip resistor 8 a mounted thereon in order tosave electricity consumed in the vibration sensor. An amplifier circuitpart 81 consisting of an FET, an operational amplifier IC and the likeis provided separately from the vibration sensor. When the amplifiercircuit part 81 is provided separately from the vibration sensor in thismanner, the circuit board 8 has only the chip resistor 8 a mountedthereon thereby to produce a large space. As a result, back chambercapacitance of the diaphragm electrode 3 increases in time ofdisplacement, thereby to improve sensor sensitivity.

With reference to FIG. 6, the above-noted circuit board 8 acts as thesecond restricting member KB as well. The circuit board 8 has an openingformed therein in order to diminish viscosity resistance (stiffness) ofthe diaphragm electrode 3 in time of displacement. In this case, it ispreferable to provide electronic parts required to be mounted on thecircuit board 8, on a surface thereof which is not opposed to the weightmember 2.

Third Embodiment

A vibration sensor according to a third embodiment of the presentinvention is different from that of the first embodiment in that thediaphragm electrode 3 includes a movable portion having a shape forabsorbing shocks.

More particularly, as shown in FIG. 7, the diaphragm electrode 3includes a corrugated portion (corrugation) 3 a between an inner portionwhere the weight member 2 is attached and an outer portion fixedlysupported. The corrugated portion 3 a is bulged away from the fixedelectrode 1 (downward in the drawing) and placed between the diaphragmelectrode 3 and the projections 2 a so as not to contact the electretlayer 5 in time of vibration. The above corrugated portion 3 a absorbsshocks applied to the diaphragm electrode 3 and improves movabilityperformance of the diaphragm electrode 3. Further, it is also possibleto increase the thickness of the diaphragm electrode 3 (increase thethickness from 2 micrometers to 4 micrometers—12 micrometers, forexample) without lowering the movability performance of the diaphragmelectrode 3, which enhances the effect of preventing damage to themembrane.

Fourth Embodiment

In a vibration sensor according to a fourth embodiment of the presentinvention, the construction for restricting displacement of the weightmember 2 in the directions along the membrane surface of the diaphragmelectrode 3 is different from that of the first embodiment.

More particularly, as shown in FIG. 8, the sensor includes limit members11 a for contacting end portions of the weight member 2 displaced alongthe direction of the membrane surface of the diaphragm electrode 3,thereby to restrict displacement of the weight member 2. The limitmembers 11 a are formed in parts opposed to the end portions of theweight member 2 to be spaced from the membrane surface of the diaphragmelectrode 3. As illustrated in FIGS. 9( a) and 9(b), the limit members11 a comprise claw-shaped portions or flange-shaped portions formed oninner peripheries of the diaphragm ring 11 in a manner similar to thefirst embodiment.

Further Embodiments

Vibration sensors according to further embodiments of the invention willbe described next.

In the foregoing embodiments, the fixed electrode 1 is formed utilizingthe inner wall of the housing 10. Instead, as shown in FIG. 10, aseparate fixed electrode 12 may be provided apart from the housing 10.The fixed electrode 12 may be supported by the housing 10 through ametal ring 13, and may have an electret layer 5 formed on the surfaceopposed to the diaphragm electrode 3. In FIG. 10( a), a limit ring 9 isprovided to act as the second restricting member KB for restrictingdisplacement of the weight member 2 in the directions perpendicular tothe membrane surface of the diaphragm electrode 3. In FIG. 10( b), thecircuit board 8 also acts as the second restricting member KB to providea low thin-back type sensor having a reduced height.

The present invention may be applied to a vibration sensor for detectingvibrations, an acceleration sensor for detecting rates of acceleration,and a vibration detecting device, an acceleration detecting device, apedometer and the like incorporating these sensors.

1. A vibration sensor comprising a fixed electrode, and a diaphragmelectrode having a weight member attached to a membrane surface facingaway from the fixed electrode and fixedly supported at peripheriesthereof, the vibration sensor being capable of outputting variations ofcapacitance between the fixed electrode and the diaphragm electrode asvibration signals, wherein the vibration sensor further comprisesprojecting portions formed on parts of an end portion of the weightmember to project along a direction of the membrane surface and spacedfrom the membrane surface of the diaphragm electrode, and a restrictingmember for contacting the projecting portions of the weight memberdisplaced along the direction of the membrane surface of the diaphragmelectrode thereby to restrict displacement of the weight member.
 2. Avibration sensor comprising a fixed electrode, and a diaphragm electrodehaving a weight member attached to a membrane surface facing away fromthe fixed electrode and fixedly supported at peripheries thereof, thevibration sensor being capable of outputting variations of capacitancebetween the fixed electrode and the diaphragm electrode as vibrationsignals, wherein the vibration sensor further comprises restrictingmembers for contacting end portion of the weight member displaced alongthe direction of the membrane surface of the diaphragm electrode,thereby to restrict displacement of the weight member, the restrictingmembers being formed on parts opposed to the end portion of the weightmember and spaced from the membrane surface of the diaphragm electrode.3. A vibration sensor as defined in claim 1 or 2, further comprising asecond restricting member for contacting a surface of the weight memberdisplaced along a direction perpendicular to the membrane surface of thediaphragm electrode, thereby to restrict displacement of the weightmember.
 4. A vibration sensor as defined in claim 3, further comprisinga circuit board having an output circuit mounted thereon for vibrationsignals, wherein the circuit board or an electronic part mounted on thecircuit board acts also as the second restricting member.